The steam generating assembly of the present invention subjects a food product, such as a sandwich bun, to a controlled burst of low pressure steam in order to quickly and uniformly raise the temperature of the food product to its desired serving temperature or higher. By raising the temperature to above the desired serving temperature, the storage time of a pre-assembled food product, such as a fast food sandwich may be extended without sacrificing the quality or freshness of the product. The invention claims a steam generating assembly for steam heating a pre-processed food product. The steam generating assembly is comprised of a steam module housing including a supply source, a steam generating heating element provided in the steam module housing, a target area in fluid communication with said steam generating heating element over which the food product may be positioned, and an actuation switch for initiating a steam delivery cycle wherein steam is released from the steam generating heating element through said target area to heat the food product.